Described herein are developer compositions. More specifically, described herein are developers comprising a high resistivity toner and optionally a high resistivity carrier.
Generally, an electrophotographic printing machine includes a photoconductive member which is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to an optical light pattern representing the document being produced. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the document. After the electrostatic latent image is formed on the photoconductive member, the image is developed by bringing a developer material into proximal contact therewith. Typically, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted to the latent image from the carrier granules and form a powder image on the photoconductive member which is subsequently transferred to a copy sheet. Finally, the copy sheet is heated or otherwise processed to permanently affix the powder image thereto in the desired image-wise configuration.
In the prior art, both interactive and non-interactive development has been accomplished with magnetic brushes. In typical interactive embodiments, the magnetic brush is in the form of a rigid cylindrical sleeve which rotates around a fixed assembly of permanent magnets. In this type of development system, the cylindrical sleeve is usually made of an electrically conductive, non-ferrous material such as aluminum or stainless steel, with its outer surface textured to control developer adhesion. The rotation of the sleeve transports magnetically adhered developer through the development zone where there is direct contact between the developer brush and the imaged surface, and charged toner particles are stripped from the passing magnetic brush filaments by the electrostatic fields of the image.
Magnetic brush development is generally described with respect to the resistivity properties of the carrier being utilized in the magnetic brush. An insulative magnetic brush utilizes a carrier with a resistivity of about 1013 to 1018 ohm-cm. A conductive magnetic brush utilizes a carrier with a resistivity of about 10−5 to 107 ohm-cm. And, a semiconductive magnetic brush utilizes a carrier with an intermediate resistivity of about 107 to 1013 ohm-cm,
U.S. Pat. No. 4,546,060, which is incorporated herein by reference, discloses an electrographic, two-component dry developer composition comprising charged toner particles and oppositely charged, magnetic carrier particles. The developer is employed in combination with a magnetic applicator comprising a rotatable magnetic core and an outer, non-magnetizable shell to develop electrostatic images.
Toners having crystalline polyester resins or semi-crystalline resins that are employed in various image development systems are known. Specifically, crystalline toners such as those taught in U.S. Patent Publication No. 2004-0142266 are known and incorporated herein by reference.
One issue with current crystalline and semi-crystalline toners and development systems comprising such toners is that they do not perform well in all humidities. It is desirable that developers be functional under all environmental conditions to enable good image quality from a printer. In other words, it is desirable for developers to function at low humidity such as a 15% relative humidity (denoted herein as C-zone) and at high humidity such as at 85% relative humidity (denoted herein as A-zone).
Toner blends containing crystalline or semi-crystalline polyester resins with an amorphous resin have been recently shown to provide very desirable ultra-low melt fusing, which is a key enabler for high-speed printing and for lower fuser power consumption. These types of toners containing crystalline polyester have been demonstrated in both emulsion aggregation (EA) toners, and in conventional jetted toners. One of the most serious issues with all toners containing crystalline or semi-crystalline polyester resins, has been the low charge in A-zone.
EA branched polyester toners containing crystalline polyesters show demonstrated ultra-low melt fusing performance, with very low minimum fixing temperature (MFT) and high gloss. However, charging performance, particularly in A-zone, has been a significant issue.
Thus, developers comprising crystalline toners that exhibit good charging in both A-zone and C-zone are still desired.